1. Field of Application
The present invention relates to an engine control apparatus for an internal combustion engine of a vehicle, and in particular to an engine control apparatus having an idling stop function.
2. Background Technology
Types of vehicle engine control apparatus are known having an idling stop function, whereby the engine is stopped automatically when the apparatus detects a first type of condition (e.g., the vehicle brakes are applied while the vehicle speed is low, or the vehicle becomes halted) and is automatically restarted when a second type of condition is detected (e.g., actuation of accelerator pedal). This serves to reduce fuel consumption, by reducing the extent of engine idling.
Motor vehicles are generally equipped with a vacuum-boost type of braking assistance system, for augmenting the force applied by the vehicle driver in depressing the brake pedal. Such a system uses a brake booster which employs the difference between atmospheric pressure and the engine intake air pressure (intake manifold pressure) while the engine is running, to generate a braking assistance force. The magnitude of that difference (a negative pressure value) is referred to in the following as the booster pressure. When the engine is stopped, a sufficient level of booster pressure will be maintained for a short time, so that braking assistance will temporarily continue.
It has been proposed, for example, in Japanese patent first publication No. 2006-83830, to detect the changes which occur in the booster pressure after the engine has become halted, and to generate a command for restarting the engine if the booster pressure is judged to have fallen below (i.e., become less negative than) a predetermined value. The reason for this proposal is to prevent a problem whereby the vehicle driver actuates the brake pedal subsequent to the engine having been automatically halted, and may feel alarmed because the normal degree of braking assistance is not being provided, due to an excessive drop in the booster pressure.
However with such a method, utilizing a pressure sensor for detecting the level of booster pressure, it is possible that the actual value of booster pressure may not be obtained, e.g., when the pressure sensor becomes defective. This may lower the detection accuracy to such an extent that, even if the booster pressure has fallen excessively, that condition will not be detected. Thus continuation of a normal degree of braking assistance, after an automatic engine stop operation, cannot be reliably ensured.